Year zero
Year zero does not exist in the system usually used to number years in the and in its predecessor, the . In this system, the year 1 BC is followed by AD 1. However, there is a year zero in (where it coincides with the Julian year 1 BC) and in (where it coincides with the Gregorian year 1 BC) as well as in all and s. Counting intervals without a zero The absence of a year 0 leads to some confusion concerning the boundaries of longer decimal intervals, such as decades and centuries. For example, the of the Gregorian calendar began on Monday, 1 January 2001, rather than the widely celebrated Saturday, 1 January 2000. Likewise, the 20th century began on 1 January 1901. This rule arose because the Gregorian calendar begins with a year 1 instead of 0. Cardinal and ordinal numbering of years is therefore identical: The year 10 is the tenth year of the calendar and the end of the first decade. The year 11 is the first year of the second decade, and so on. In spite of this rule, years ending in 0, rather than 1, are commonly perceived as marking the beginning of a new decade, century, or millennium.Today most people accept the logic of centuries beginning in years marked '00. Decades, however, are more used as a collective term (e.g. the 1930s) rather than a periodic term (e.g. 1930–1939). Historical, astronomical and ISO year numbering systems Historians The era was introduced in 525 by (c.470–c.544), who used it to identify the years on his . He introduced the new era to avoid using the Diocletian era, based on the accession of Emperor , as he did not wish to continue the memory of a persecutor of Christians. In the preface to his Easter table, Dionysius stated that the "present year" was "the of Probus Junior Probus" which was also 525 years "since the incarnation of our Lord ".Nineteen year cycle of Dionysius How he arrived at that number is unknown. Dionysius did not use AD years to date any historical event. This began with the English cleric (c. 672–735), who used AD years in his (731), popularizing the era. Bede also used a term similar to the English once, but that practice did not catch on until very much later. Bede did not sequentially number , weeks of the year, or months of the year, however, he did number many of the using a counting origin of one in . Previous Christian histories used ("in the year of the world") beginning on the first day of , or anno Adami ("in the year of ") beginning at the creation of Adam five days later (the sixth day of creation according to the ), used by Africanus, or anno Abrahami ("in the year of ") beginning 3,412 years after Creation according to the , used by , all of which assigned "one" to the year beginning at Creation, or the creation of Adam, or the birth of Abraham, respectively. Bede continued this earlier tradition relative to the AD era. In chapter II of book I of Ecclesiastical history, Bede stated that invaded Britain "in the year 693 after the building of Rome, but the sixtieth year before the incarnation of our Lord", while stating in chapter III, "in the year of Rome 798, " also invaded Britain and "within a very few days concluded the war in the fortysixth year from the incarnation of our Lord".Ecclesiastical History of the English Nation Although both dates are wrong, they are sufficient to conclude that Bede did not include a year zero between BC and AD: 798 − 693 + 1 (because the years are inclusive) = 106, but 60 + 46 = 106, which leaves no room for a year zero. The modern English term "before Christ" (BC) is only a rough equivalent, not a direct translation, of Bede's Latin phrase ante incarnationis dominicae tempus ("before the time of the lord's incarnation"), which was itself never abbreviated. Bede's singular use of 'BC' continued to be used sporadically throughout the . It is often incorrectly stated that Bede did not use a year zero because he did not know about the number zero. Although the for zero ( ) did not enter Europe until the eleventh century, and had no symbol for zero, Bede and Dionysius Exiguus did use a word, nulla meaning "nothing", alongside Roman numerals or Latin number words wherever a modern zero would have been used.Faith Wallis, trans. Bede: The Reckoning of Time (725), Liverpool: Liverpool Univ. Pr., 2004. ISBN 0-85323-693-3.Byrhtferth's Enchiridion (1016). Edited by Peter S. Baker and Michael Lapidge. Early English Text Society 1995. ISBN 978-0-19-722416-8. The anno Domini nomenclature was not widely used in Western Europe until the 9th century, and the 1 January to 31 December historical year was not uniform throughout Western Europe until 1752. The first extensive use (hundreds of times) of 'BC' occurred in Fasciculus Temporum by in 1474, alongside years of the world (anno mundi).Werner Rolevinck, Fasciculus temporum. The terms anno Domini, Dionysian era, Christian era, vulgar era, and common era were used interchangeably between the and the 19th century, at least in . But vulgar era was suppressed in English at the beginning of the 20th century after vulgar acquired the meaning of "offensively coarse", replacing its original meaning of "common" or "ordinary". Consequently, historians regard all these eras as equal. Historians have never included a year zero. This means that between, for example, 1 January 500 BC and 1 January AD 500, there are 999 years: 500 years BC, and 499 years AD preceding 500. In common usage anno Domini 1 is preceded by the year 1 , without an intervening year zero.While it is increasingly common to place AD after a date by analogy to the use of BC, formal English usage adheres to the traditional practice of placing the abbreviation before the year as in Latin (e.g., 100 BC, but AD 100). Thus the year 2006 actually signifies "the 2006th year". Neither the choice of calendar system (whether or ) nor the era (Anno Domini or ) determines whether a year zero will be used. If writers do not use the convention of their group (historians or astronomers), they must explicitly state whether they include a year 0 in their count of years, otherwise their historical dates will be misunderstood. No historian includes a year 0 when numbering years in the current standard era.V. Grumel, La chronologie (1958), page 30. Astronomers To simplify calculations, s have used a defined leap year zero equal to of the traditional Christian era since the Modern astronomers do not use years for intervals because years do not distinguish between common years and leap years, causing the resulting interval to be inaccurate. In astronomy, the numbering of all years labeled Anno Domini remain unchanged. However, the numerical value of years labeled Before Christ are reduced by one by the insertion of a year 0 before . Thus, astronomical BC years and historical BC years are not equivalent. To avoid this confusion, modern astronomers label years as positive or negative, instead of BC or AD. The current method was created by , who explained: In this quote, Cassini used "year" as both a calendar year and as an instant before a year. He identified the calendar year 0 as the year during which Jesus Christ was born (on the traditional date of , and as calendar leap years divisible by 4 (having an extra day in February). But "the sum of years before and after Jesus Christ" referred to the years between a number of instants at the beginning of those years, including the beginning of year 0, identified by Cassini as "Jesus Christ", virtually identical to Kepler's "Christi". Consider the three instants ('years') labeled by Cassini, which modern astronomers would label . Cassini specified that his end years must be added, so the interval between the instants (noon ) and is , but modern astronomers would subtract their 'years', , which agrees with Cassini. The calendar years between these two instants would be and , leaving the calendar year beginning at +1.0 outside the interval. Astronomical notation Astronomers use year numbers not only to identify a calendar year (when placed alongside a month and a day number) but also to identify a certain instant (known in astronomy as an ). To identify an instant, astronomers add a number of fractional decimal digits to the year number, as required for the desired precision: thus designates noon (Gregorian), and 1992.5 is exactly 7.5 years of 365.25 days each earlier, which is the instant (Gregorian). Similarly, J1996.25 is 3.75 before J2000.0, which is the instant , one-quarter of a year after the instant J1996.0 = . In this notation, J0000.0 is noon of (Julian), and J0001.0 is 18:00 on (Julian). This astronomical notation is called Julian epoch and was introduced in 1984; before that time, astronomical year numbers with decimal fractions referred to s and were written without a letter prefix. During the astronomers began to change from named eras to numerical signs, with some astronomers using BC/0/AD years while others used years. By the mid all astronomers were using years. Numerical signs effectively form a new era, reducing the confusion inherent in any date which uses an astronomical year with an era named Before Christ. History of astronomical usage In 1849 the English astronomer invented s, which are a sequence of numbered days and fractions thereof since noon , which was Julian date 0.0. Julian dates count the days between two instants, automatically accounting for years with different lengths, while allowing for any arbitrary precision by including as many fractional decimal digits as necessary. The modern mathematical astronomer no longer mentions determining intervals via years, stating:Jean Meeus, Astronomical algorithms (Richmond, Virginia: Willmann-Bell, 1991) 60. In the astronomical sequence, however, these leap-years are called and the rule of divisibility by 4 subsists.|Jean Meeus|''Astronomical algorithms''}} In 1627 the German astronomer first used an astronomical year which was to become year zero in his . He labeled the year Christi and inserted it between years labeled Ante Christum (BC) and Post Christum (AD) on the mean motion pages of the Sun, Moon, and planets.Tabulae Rudolphinae – Ioannes Keplerus (1627) 191 (42), 197 (48), 203 (54), 209 (60), 215 (66), 221 (72), 227 (78). Then in 1702 the French astronomer used a year he labeled at the end of years labeled ante Christum (BC), immediately before years labeled post Christum (AD) on the mean motion pages in his Tabulæ Astronomicæ, thus adding the designation 0'' to Kepler's ''Christi.Tabulae Astronomicae – Philippo de la Hire (1702), Tabulæ 15, 21, 39, 47, 55, 63, 71; Usus tabularum 4. Finally, in 1740 the French astronomer , who is traditionally credited with the invention of year zero,Robert Kaplan, [http://books.google.com/books?id=Bn0EBVsfi1YC&pg=PA103&lpg=PA103 The nothing that is] (Oxford: Oxford University Press, 2000) 103. completed the transition in his Tables astronomiques, simply labeling this year 0'', which he placed at the end of years labeled ''avant Jesus-Christ (BC), immediately before years labeled après Jesus-Christ (AD).Jacques Cassini, Tables astronomiques (1740), Explication et usage 5; Tables 10, 22, 53. ISO 8601 (and previously ISO 8601:2000, but not ISO 8601:1988) explicitly uses astronomical year numbering in its date reference systems. Because it also specifies the use of the for all years before 1582, some readers incorrectly assume that a year zero is also included in that proleptic calendar, but it is not used with the BC/AD era. The "basic" format for year 0 is the four-digit form 0000, which equals the historical year 1 BC. Several "expanded" formats are possible: -0000 and +0000, as well as five- and six-digit versions. Earlier years are also negative four-, five- or six-digit years, which have an one less than the equivalent BC year, hence -0001 = 2 BC. Because only (7-bit ) characters are allowed by ISO 8601, the minus sign is represented by a . Other traditions South Asian calendars All eras used with and s, such as the or the , begin with the year 0. All these calendars use elapsed, expired, or complete years, in contrast with most other calendars which use current years. A complete year had not yet elapsed for any date in the initial year of the epoch, thus the number 1 cannot be used. Instead, during the first year the indication of 0 years (elapsed) is given in order to show that the epoch is less than 1 year old. This is similar to the Western method of stating a person's age – people do not reach age one until one year has elapsed since birth (but their age during the year beginning at birth is specified in months or fractional years, not as age zero). However if ages were specified in years and months, such a person would be said to be, for example, 0 years and 6 months or 0.5 years old. This is analogous to the way time is shown on a : during the first hour of a day, the time elapsed is 0 hours, n minutes. Maya historiography Many historians, but not all, assume (or used to assume) that a year 0 exists in the modern calendar and thus specify that the epoch of the occurred in 3113 BC rather than 3114 BC. This would require the sequence 1 BC, 0, AD 1 as in early astronomical years.Linda Schele, The proceedings of the Maya hieroglyphic workshop (Austin, Texas, 1992) page 173. In popular culture *'' , a , , game. *In the film '' , Leonardo DiCaprio's character is, during his mental instability, crazed about the term Year 0. *''Year Zero'' is a theatrical play that highlights the everyday struggles of a Cambodian-American family.[http://www.theatreinchicago.com/playdetail.php?playID=3244 Year Zero Play Details]Year Zero Playbill (See .) *The fictitious theologian 's most famous work relates to the year 0: a 1927 dissertation submission to the University of Worms entitled "The Problem of the Year 0". *''Germany, Year Zero'' is a 1948 film directed by set in post-WWII Germany. *''Tokyo Year Zero'' is a novel by English author set in post-WWII Tokyo which depicts the by the . *The 1985 film Back to the Future shows the date December 25 0000 on the time circuits display of the DeLorean time machine as a joke and example of choice for witnessing the birth of Christ. * "Year Zero" is an album by the industrial rock group Nine Inch Nails, and is a concept album and Alternate Reality Game based on a post-apocalyptic earth. References Category:Zero-based numbering